The present invention relates to a magnetic disc apparatus, and more particularly to a magnetic disc apparatus having swing head arms.
Recently, with the advances made in high density recording, a magnetic disc apparatus has been required to have much higher reliability.
In a magnetic disc apparatus of a type having a swing head arm, the following is required.
(1) To prevent any damage to data recorded, a magnetic head of a floating type should not come into contact with a read and write zone on a magnetic disc. PA1 (2) To perform a seek operation in a stable manner, the load counter to swing a head arm about a center shaft should be constant, irrespective of rotational positions thereof.
Japanese Laid-Open Patent Applications No.60-5479 and No.62-244266 respectively disclose magnetic disc apparatuses of a swing head arm type which are adapted so that, when electric power is shut off unexpectedly during a read/write mode, a head arm is turned thereby to shift a magnetic head to a contact start stop zone on a magnetic disc.
Since the magnetic head is returned rapidly to the contact start stop zone, the magnetic head does not come into contact with a read and write zone on the magnetic disc, and thereby any data damage can be prevented.
Generally, the swing head arm has moment of force due to deviation of the center of gravity of the head arm itself with respect to a center shaft. Further, on the swing head arm a force of wind acts generated due to high speed rotation of the magnetic disc and the resilience force of a flexible print circuit connected to the head arm.
Accordingly, moment of force of the head arm is not constant but varies depending on the rotational position thereof.
The above magnetic disc apparatuses of Japanese Laid-Open Patent Applications No.60-5479 and No.62-244266 are not of a construction wherein moment of force of the head arm is made constant irrespective of rotational position thereof.
Therefore, in order to perform a seek operation at a predetermined velocity, it becomes necessary to control the level of a bias current fed to a motor for driving the head arm so as to vary the bias current according to the rotational position of the head arm. Accordingly, control of the motor for the head arm becomes inevitably complicated.